An LED device has high reliability, longevity, high luminous efficacy, and high-speed responsiveness as compared with already-existing light sources such as a white lamp, and high-intensity discharge tube, and further has various advantages such as attainable size reduction, and weight reduction, and the like. For this reason, the LED device receives attention as lighting fixture, and is now put to practical use.
In the LED device, an n-type compound-semiconductor layer configured to inject electrons into a luminous layer, and a p-type compound-semiconductor layer configured to inject positive holes into the luminous layer are arranged on a substrate with a luminous layer formed of a compound semiconductor interposed between these compound-semiconductor layers, and the electrons and the positive holes recombine with each other in the luminous layer, whereby light is emitted. Above all, as an LED device capable of emitting white light, a device having a structure provided with an n-type GaN layer, GaN-based luminous layer, and p-type GaN layer receives attention.
Such a GaN-based LED device is, heretofore, manufactured by the method described below.
An n-type GaN layer, GaN-based luminous layer, and p-type GaN layer are stacked in this order on the surface of a substrate, thereby forming a laminated semiconductor layer. A predetermined resist pattern is formed on the laminated semiconductor layer. The laminated semiconductor layer is subjected to reactive ion etching using the resist pattern as a mask, and using, for example, chlorine gas as an etching gas so that the n-type GaN layer remains to have a predetermined thickness on a surface of the substrate. Thereby, an LED element structure part having, for example, a rectangular external shape, and an electrode connection region (contact region) integrated with the n-type GaN layer of the structure part concerned and positioned in the rectangular LED element structure part are formed. Thereafter, the resist pattern is removed.
However, after the resist pattern is removed, residual substance including a polymer, carbonaceous matter, and the like mainly originating from the resist is attached to the surface of the p-type GaN layer which is the uppermost layer of LED element structure part, and on which the resist pattern has been positioned. Further, a residual substance such as an altered layer or the like originating from an oxide of a constituent element of GaN is attached to the LED element structure part provided with the n-type GaN layer, GaN-based luminous layer, and p-type GaN layer in such a manner that the residual substance protrudes from the lateral side of the LED element structure part in the direction to the part at which the resist pattern has existed. Moreover, the residual substance of the altered layer or the like is also attached to the surface of the contact region integrated with the n-type GaN layer in the vicinity of the lateral side of the LED element structure part.
If the residual substance is attached to the surface of the p-type GaN layer of the uppermost layer, when an electrode is formed on the surface of the p-type GaN layer in the subsequent process, the connection resistance of the electrode is increased. Further, if the residual substance is attached to the lateral side ranging over the n-type GaN layer, GaN-based luminous layer, and p-type GaN layer, the efficiency in injecting electrons from the n-type GaN layer into the luminous layer, and the efficiency in injecting positive holes from the p-type GaN layer into the luminous layer are disturbed, and the luminous efficacy is lowered.
Such being the case, heretofore, removing the residual substance by treating the substrate including the LED element structure part obtained after the resist pattern is removed with Clean Strip MF (trade name of a product of Tokyo Ohka Kogyo Co., LTD.) containing an aromatic hydrocarbon, alkylbenzene sulfonic acid, and nonyl phenol is carried out.